1. Field of the Invention
This invention relates to a manifold to which a tube may be coupled, and to a method for coupling the tube and the manifold. In particular, the invention relates to a detonation manifold for a separation device.
Separation devices are used when it is desired to effect a separation of two structures that were previously adjoined to one another. Such devices join the structures to be separated and are later ruptured along a separation line to release the structures from one another. A separation device with which the present invention may be used typically comprises a frangible joint within which is disposed an expansion member. The frangible joint comprises a pair of joinder flanges interconnected by a release portion. Typically, the release portion comprises a channel within which the expansion member is disposed, and there is a groove disposed along the channel to provide a fracture seam. The expansion member comprises a deformable containment tube within which an elastomeric charge holder supports a linear explosive charge, typically a mild detonation fuse. Before separation, the joinder flanges are secured to respective structures, e.g., a fairing or a field joint adapter on a rocket, missile or payload platform, that are to be separated, and the release portion keeps the assembly together.
It is known to couple the linear explosive charge to an initiation device through the use of a detonation manifold. Detonation of the initiation device then initiates the linear explosive charge, which deforms the expansion tube and thus fractures the release portion of the frangible joint along the groove to separate the structures. The containment tube prevents the release of shrapnel and of chemical by-products of the detonation of the charge in the expansion member, thus preventing damage to the structures or objects therein from shrapnel or other detonation by-products.
2. Related Art
U.S. Pat. No. 5,331,894 to Wassell et al, dated Jul. 26, 1994, states that a conventional flange may be dimensioned and configured to have a circular external cross-sectional configuration. To engage the containment tube to the flange, the end of the tube is flared to a circular configuration. The tube is then crimped circumferentially about the flange in a roll crimp procedure. It is further necessary to secure the circular crimps with retaining bands to assure that the crimps will not be undone upon detonation of the cord (see column 1, line 46 through column 2, line 2). This suggests that the flange has a generally uniform, i.e., non-tapered, axial configuration. The invention of U.S. Pat. No. 5,331,894 is represented herein in FIGS. 1A, 1B and 1C.
As seen in FIG. 1A, conventional separation device (23) comprises an expansion member (10) disposed within a frangible joint (24). Frangible joint (24) may comprise an extruded aluminum member having a release portion comprising separation walls (26a, 26b) and joinder flanges (27a, 27b) mounted to the release portion for attachment to the structures to be separably attached. Thus, prior to separation, frangible joint (24) functions like a butt plate. Separation walls (26a, 26b) also serve to define an internal channel (unnumbered) for receiving expansion member (10). Expansion member (10) comprises a containment tube (20) within which is disposed an elastomeric charge holder (18). Within holder (18) is disposed a linear detonatable charge such as a mild detonation fuse (16). One suitable detonation fuse is known under the designation HNS-IIA Mild Detonating Fuse. Such a fuse typically contains a core of 24 grains per linear foot hexanitrostilbene (HNS) in an aluminum jacket. However, other detonation materials such as cyclotetramethylene tetranitramine (HMX) can be used as well. The elastomeric charge holder (18) may comprise a silicone polymer. Containment tube (20) is made of a material like stainless steel that is sufficiently ductile to deform when fuse (16) detonates, but is also strong enough not to fracture or be perforated by shrapnel released by fuse (16), and so contains the debris and other detonation products released by fuse (16) upon detonation. Generally, expansion member (10) is inserted lengthwise into the channel formed in frangible joint (24). Walls (26a, 26b) have fracture grooves (28a, 28b) that are designed to provide a clean fracture of walls (26a, 26b) along the length of the separation device in response to expansion of the expansion member (10) upon detonation of fuse (16). Thus, joinder flanges (27a, 27b) and their associated structures are separated upon detonation of the detonation fuse.
A conventional detonation manifold for use with the separation device (23) of FIG. 1A is seen in FIG. 1B. Manifold (30) includes a body portion (31) having initiation ports (32) for receiving a primary and a secondary initiation device. Detonation manifold (30) includes a mounting flange (34) formed with mounting holes (36) that allow manifold (30) to be attached to one of the structures to be separated. A coupling boss (38) is mounted on body portion (31). Boss (38) has a bore (40) that communicates with initiation port (32) so that a detonation fuse may be passed therethrough into detonation relation with the initiation device in initiation port (32). Coupling boss (38) has a generally oval cross section, with a major axis (42) and a minor axis (44). Boss (38), however, is generally uniform, i.e., it is not tapered, in the axial direction, and has notches (46) that facilitate the use of stake crimps to help fasten tube (20) onto boss (38).
To facilitate joinder of an expansion member to detonation manifold (30) as shown in FIG. 1C, the expansion member is extended out of frangible joint (24) and a portion of the elastomeric charge holder (18) is removed from within the containment tube (20). Before detonation fuse (16) is inserted into bore (40) (FIG. 1B), a booster cap (41) is attached to its end. Such a booster cap may comprise, e.g., a charge of about 96 mg of an HNS-IIA explosive. Tube (20) is initially coupled to boss (38) by a stake crimp (48). A multi-piece locking collar (50) clamps the containment tube (20) to the boss (38), but it does so without force in the direction of the adjacent body portion (31) of manifold (30), and without being able to provide clamping force upon tube (20) about the entire circumference of the tube. Specifically, no radial force is applied to the tube at the point where the pieces of collar (50) mate.
Since the coupling boss (38) and tube (20) are both formed from hard metals and because it is difficult to flare tube (20) into a non-tapered configuration for a good fit on boss (38), this prior art device does not produce plastic deformation of the tube or boss materials, so a good seal between them is not achieved, and gaps often occur between them. Such gaps can be filled by adhesives or sealants, but such materials are not strong enough to survive the transient high pressures that result when the separation device is initiated.